Autism Spectrum Disorders (ASD) are one of the most commonly occurring neuro- developmental disorders, affecting 1 in 68 children, frequently resulting in impairments in the functional skills necessary for independent living, and presenting a significant impact on families and society. Up to 90% of individuals with ASD present with difficulties processing and integrating sensory information and these have been shown to be a significant factor impacting functional skills. Intervention for these sensory issues is one of the most highly requested treatments. We have showed that children with ASD and sensory issues who were randomized to a 30-session Sensory Integration Treatment (SIT) made significant gains in functional skills, showed reduced sensory-related maladaptive behaviors, and improved their participation in daily activities compared to controls. Now that we have evidence in support of SIT for improvement of functional skills in this group of children with sensory issues, we seek to compare the effectiveness of SIT to focused behavioral strategies on improvement of functional skills for children with ASD and sensory issues ages 6-8.5 years of age. Importantly, we will interrogate the mechanisms of action and the phenotypic characteristics that predict response to intervention. After a comprehensive phenotypic assessment, eligible participants will be randomized to 30 one-hour sessions of SIT, ABA or No Treatment (NT). Outcome assessment, which includes behavioral and electrophysiological measures, will occur at baseline, post treatment and at 12 weeks following treatment to assess sustainability. The specific aims of the study are to: 1) compare 30 session SIT to the same dosage of ABA to evaluate immediate and sustained changes in functional skills and maladaptive behaviors; 2) to assess whether the treatment regimen has differential effects on sensory processing and multisensory integration functions; and 3) to determine whether autism severity, cognitive level or severity of sensory symptoms moderate intervention outcomes. This study addresses multiple priorities of the Interagency Autism Coordinating Council's Strategic Plan for research including the need for comparative effectiveness RCTs of interventions for ASD, studies to uncover the biological mechanisms of ASD symptoms to aid in the development of customized, targeted interventions, identification of mediators or moderators of interventions, and treatment of core deficits. Findings will inform parents and providers about interventions that may best help improve functional skills based on phenotypic characteristics and symptoms. A team of inter-disciplinary researchers and clinicians with complementary expertise is utilized to address this unmet need.